Unify language definitions

[Xanewok]

At the moment we have three separate ways to define the language:

1. YAML spec (aka v0)
2. DSL v1
3. DSL v2

Over the time, the definitions became slightly divergent, which is problematic since there are now different sources of truth. We plan to migrate to DSL v2 (#638, #637), however we need to settle on the final definition in the process. This issue should track any divergences and how we plan to resolve them.

It's worth noting that unifying the definition in a specific way (e.g. by re-introducing the List suffix for lists in DSL v2) does not prevent us from rolling back the unifying change for (all of the) language definition at some point; we only care about unification here.

The main goal is to agree on the unified, correct definition using the least amount of effort. Once we have that, we can proceed with #637, #638, and then be free to change or update the definition only once.

Known differences

• Inline the (Yul)Statement parser in v0/v1 #658
• (Yul)Statement ordered choice definition is different (affects error recovery) (done in Fix some language definitions in DSL v1/v2 #653)
• Specify Optional(NonEmpty(List)) in v2 where we do in v1 #668
• Some types are introduced in v2 to work around the fact that it's not possible to specify Optional inline:
  • VariableDeclarationValue
  • TupleValue
  • UsingAlias
  • ImportAlias
  • more?
• Drop List suffix from some repeated nodes in v0/v1 #660
• Backport {Uint,Int,Fixed,Ufixed}Keyword from DSL v2 to v0/v1 #662
• {Error,Event}ParametersDeclaration defined in v2 but not in v0/v1 (done in Fix some language definitions in DSL v1/v2 #653)
• Retrofit {Hex,Decimal}NumberExpression from v2 into v0/v1 spec #657
• Forbid some empty separated lists in v2 #667

These change the CST shape for our parser as shown in #650, so we should tackle most (if not all) of these until we can proceed with that PR.

Recent pull requests that have helped with this:

• fix trailing IdentifierPart in grammar #641
• fix: Define DecimalLiteral in DSL v2 using the DSL v1 rules #643
• Reserve keywords more correctly in DSL v1 #644
• fix: Specify YulBlock as delimited by braces in DSL v2 #645
• use v1 grammar for string literals #646
• fix: Enable destructuring in UsingFor statement since 0.8.13 #649

[Xanewok]

A lot was done to unify the language definitions in the meantime; with #637 done we will have only a single (and thus unified) definition.

[Xanewok]

The DSL v2 is treated as our source of truth with v0 slated for removal as part of #637, so I'll be closing this one for clarity (not much to be done in terms of unification; we just need to remove the old v0). @OmarTawfik Feel free to re-open if that's not the case.